1. Field of the Invention
The present invention relates to a method and to a device for determining the internal resistance of a battery cell of a battery, in particular a traction battery.
2. Description of the Related Art
It is becoming apparent that in the future new battery systems will increasingly be used both in stationary applications, e.g. wind power installations, and also in vehicles, e.g. in hybrid and electric vehicles. In the present application, the terms “battery” and “battery system” will be used for “accumulator” or “accumulator system,” in accordance with everyday usage.
The functional design of a battery system known from the prior art is shown in FIG. 2. In order to achieve the required power and energy data with the battery system, in a battery cell 1 individual battery cells 1a are connected in series, and partly also in parallel.
Between battery cells 1a and the poles of the battery system there is situated a so-called safety and fuse unit 16 that is used for example to connect and disconnect battery 1 to external systems and to protect the battery system against impermissibly high currents and voltages, as well as providing safety functions such as the single-pole separation of battery cells 1a from the battery system poles when the battery housing is opened. A further functional unit is formed by battery management system 17, which, alongside battery state recognition system 17a, also carries out the communication with other systems, as well as the thermal management of battery 1.
Battery state recognition functional unit 17a shown in FIG. 2 has the task of determining the current state of battery 1 and of forecasting the future behavior of battery 1, e.g. providing a battery life forecast and/or a range forecast. The forecasting of future behavior is also referred to as prediction. The design of a model-based battery state recognition system is shown in FIG. 3. The depicted model-based battery state recognition and prediction system is based on an evaluation of the electrical quantities battery current and battery voltage, as well as the temperature of battery 1, using an observer 17b and a battery model 17c in a known manner. The battery state recognition can be carried out for individual cells 1a of a battery 1, this recognition then taking place on the basis of the corresponding cell voltage, the cell current, and the cell temperature. In addition, the battery state recognition can also be carried out for the overall battery 1. Depending on the desired degree of precision, this then takes place either through evaluation of the states of the individual cells 1a of battery 1 and an aggregation based thereon for the overall battery 1, or directly by evaluating the overall battery voltage, the battery current, and the battery temperature. In all the methods known from the prior art, the current courses, voltage courses, and temperature courses that occur during normal operation of battery 1 are used to determine the battery state and to predict the future behavior.